High peak-to-average ratio signals for high data-rate communication require power amplifiers to operate in a wide back-off mode, resulting in low average efficiency. Outphasing power amplifiers (PAs) use multiple amplifiers to provide output power in a linear and efficient way at the back-off condition when it is used with non-isolating power combiners.
One example of a non-isolating power combiner is the Chireix combiner. FIG. 1 illustrates two variations of an outphasing power amplifier (PA) with a Chireix combiner and input phase modulator. At 100 is a Chireix combiner using two quarter wave length transmission lines (2-way) and shunt reactive elements. These shunt elements can be replaced by transmission lines of different lengths with similar functionality as shown in the Chireix combiner at 110.
Another conventional example of an outphasing PA employs four power amplifiers with a 4-way power combiner that results in flatter efficiency over a wider back-off operation range. When these amplifiers are used in an outphasing mode with a combiner requires an input signal splitter or phase modulator such as those depicted in the Chireix combiners of FIG. 1. These signal splitters have been conventionally implemented using digital signal processing (DSP), up-converting a baseband signal to out-phased RF signals.